A power tool, for example, an electric saw, is an important tool in production and daily life of people, for forest harvesting, bucking, lopping and wood sawing. At present, an electric saw powered by combusting gasoline is cumbersome, gasoline-consuming and heavily polluting in field operations. Furthermore, an electric saw is generally started with no load, and starts cutting after outputting a relatively high torque. During cutting of the electric saw, a sawing blade thereof rapidly rubs against materials such as wood, and if there is a knur in the wood, the electric saw may occasionally jam when sawing the knur. In this case, the sawing blade of the electric saw is clamped in the wood, and it is hard to restart the electric saw in a clamped status. The sawing blade of the electric saw has to be taken out from the clamping wood, such that the electric saw is in a no-load status and restarts to continue cutting the wood. The operations are complex, operating efficiency is low, and workloads of workers are increased.